The The Size of this Universe – from Śrīmad-Bhāgavatam 3.11.40-42 

SB 3.11.40This phenomenal material world is expanded to a diameter of four billion miles, as a combination of eight material elements transformed into sixteen further categories, within and without, as follows.

The analytical studies of the material world are the subject matter of Sāṅkhya philosophy. The first sixteen diversities are the eleven senses and five sense objects, and the eight elements are the gross and subtle matter, namely earth, water, fire, air, sky, mind, intelligence and ego. All these combined together are distributed throughout the entire universe, which extends diametrically to four billion miles. Besides this universe of our experience, there are innumerable other universes. Some of them are bigger than the present one, and all of them are clustered together under similar material elements as described below.

SB 3.11.41The layers or elements covering the universes are each ten times thicker than the one before, and all the universes clustered together appear like atoms in a huge combination.

The coverings of the universes are also constituted of the elements of earth, water, fire, air and ether, and each is ten times thicker than the one before. The first covering of the universe is earth, and it is ten times thicker than the universe itself. If the universe is four billion miles in size, then the size of the earthly covering of the universe is four billion times ten. The covering of water is ten times greater than the earthly covering, the covering of fire is ten times greater than the watery covering, the covering of air is ten times greater than that of the fire, the covering of ether is ten times greater still than that of air, and so on. The universe within the coverings of matter appears to be like an atom in comparison to the coverings, and the number of universes is unknown even to those who can estimate the coverings of the universes.

SB 3.11.42The Supreme Personality of Godhead, Śrī Kṛṣṇa, is therefore said to be the original cause of all causes. Thus the spiritual abode of Viṣṇu is eternal without a doubt, and it is also the abode of Mahā-Viṣṇu, the origin of all manifestations.

Lord Mahā-Viṣṇu, who is resting in yoga-nidrā on the Causal Ocean and creating innumerable universes by His breathing process, only temporarily appears in the mahat-tattva for the temporary manifestation of the material worlds. He is a plenary portion of Lord Śrī Kṛṣṇa, and thus although He is nondifferent from Lord Kṛṣṇa, His formal appearance in the material world as an incarnation is temporary. The original form of the Personality of Godhead is actually the svarūpa, or real form, and He eternally resides in the Vaikuṇṭha world (Viṣṇuloka). The word mahātmanaḥ is used here to indicate Mahā-Viṣṇu, and His real manifestation is Lord Kṛṣṇa, who is called parama, as confirmed in the Brahma-saṁhitā:

īśvaraḥ paramaḥ kṛṣṇaḥ
anādir ādir govindaḥ

“The Supreme Lord is Kṛṣṇa, the original Personality of Godhead, known as Govinda. His form is eternal, full of bliss and knowledge, and He is the original cause of all causes